When '-F' option is used, the target directory needs to be unlinked.
Currently, the modified target ("target/source") is being unlinked, and
since it doesn't yet exist, the original target isn't removed.
This is fixed by saving the original target in target_dir and later
unlinking `target_dir` instead of unlinking the modified target.
Hence, a symbolic link (with the same name as of the original target) to
the source_file is produced.
Update the test for ln(1) to reflect fix for option '-F'
PR: 219943